Evolving environmental regulations and sensitivities provide a constant impetus to provide improved waste management systems and techniques. In particular, there is a call for improved methods of treating ground water, open bodies of water, and wetlands. Presently, agricultural practices account for the largest single contribution to non-point source pollution. Run-off from cropland, pastures, feedlots, and farmsteads continues to add substantial inputs of nitrogen and phosphorus to the nation's waterways and groundwater.
Wetlands, both natural and constructed, have been shown to be capable of remediating contaminated water, such as water from agricultural runoff or animal wastewater. The use of artificially constructed wetlands to retain and remove pollutants is steadily increasing. New applications, technological enhancements, and geographical dispersion of constructed wetlands are occurring. These systems are categorized into two basic types of constructed wetlands, Free Water Surface (FWS) systems and Subsurface Flow (SSF) systems. These wetland systems have been shown to be successful in the treatment of water.
For domestic wastewater treatment, the pollutants of most concern that may be treated with wetland systems exhibit undesirable total suspended solids (TSS), biochemical oxygen demand (BOD), total phosphorous (TP), total nitrogen (TN), and/or fecal coliform. Constructed wetlands may be particularly useful in lowering ammonia and nitrogen concentrations in water from agriculture. Nitrogen transformations in wetlands are a complex assortment of processes mediated by microbes, including nitrification, denitrification, nitrate reduction, and nitrogen fixation. In nitrification, ammonia is oxidized to nitrite, which is subsequently oxidized to nitrate. Different microorganisms are involved in each of these steps. The organisms that convert nitrite to nitrate are typically faster than the microbes that convert ammonia to nitrite. Nitrates and nitrites are reduced by bacteria to yield nitrous oxide and nitric oxide in a process known as denitrification.
Nitrous and nitric oxides within the water are further reduced to harmless nitrogen gas by surface vegetation. Elimination of the nitrogen oxides alters the ammonia-nitrogen equilibrium within the wetland system and indirectly causes increased nitrification of ammonia. Surface vegetation that is particular adapted for wetland conditions and provides good conversion of nitrogen oxides to nitrogen include such plants as cattails and bulrush.
Artificial wetlands are preferably constructed on flat or slightly-sloping landscapes where the water table consistently resides slightly above or slightly below the surface of the soil. However, there are many circumstances when relatively flat terrain is unavailable and wastewater must be contained in ponds or lagoons. Surface vegetation cannot grow in the depths of such ponds and lagoons, therefore conversion of nitrogen oxides to free nitrogen is impeded. Soil, sand, or gravel berms could be created in order to provide a basis for the surface vegetation, but construction of large berms is expensive and labor intensive.
There is a need to provide a basis for the growth of wetland surface vegetation in, on, or around wastewater lagoons such that surface vegetation may be adequately maintained within the wetland system to provide for elimination of nitrogen oxides. It is further desired to provide a basis for the growth of surface vegetation that is economical, easily constructed, and easy to maintain.